1. Field of the Invention
The present invention relates to a noise cancellation mechanism in an image sensing field, and more particularly, to a method and an apparatus for reducing fixed pattern noise of an image sensor.
2. Description of the Prior Art
Generally speaking, non-ideal effects of analog circuits exist in a traditional image sensor to make noise commonly appear on an image sensing frame. For example, the noise caused by non-ideal effects of analog circuits may include fixed pattern noise appearing on a frame, that is, vertical stripe phenomenon appearing on a sensing frame. Because a traditional sensor array may have different extents of leakage currents in different column-line circuits, inconsistent signal characteristics appear on different column-line circuits, and consequently, vertical stripe phenomenon appears on a final sensing frame. In addition, the stray capacitance in a traditional image sensor may easily make each column-line circuit suffer from interference when analog signals are switching, and thus may create inconsistent signal characteristics for different column-line circuit, which is one of the contributors to the fixed pattern noise. Moreover, there is other noise (e.g. random noise) existing in the analog circuits of a traditional image sensor that affects image sensing frames. In order to reduce the noise caused by non-ideal effects of analog circuits, the existing techniques usually implement a noise cancellation circuit in an analog domain to reduce noise. However, these kinds of circuit designs are over-complicated, and the costs of these kinds of circuits are also higher.